Allow Safe Labels, fixed #131

[tacman]

Allows HTML labels, like dividers.

[kevinpapst]

That is a potentially risk for people, who use the bundle in an environment where the menu items are user generated.
I don't think this should be activated by default.
Either you add a configuration for it, with default = false or you simply overwrite the template in your app through bundle inheritance.

The configuration would be better, because then it is compatible with the upcoming AdminLTE v3.

[kevinpapst]

Simply add a safe_labels boolean node to https://github.com/kevinpapst/AdminLTEBundle/blob/master/DependencyInjection/Configuration.php#L116
and then use "allow_safe_labels": admin_lte_context.knp_menu.safe_labels

[kevinpapst]

Thanks, I finally tested it and it indeed safe to set. Thank you @tacman